1. Field of the Invention
The present invention relates to a color recording method and a color printer for performing color recording by means of YMC signals, and particularly to a color recording method and a color printer for performing color recording by generating YMC signals from inputted RGB signals.
2. Description of the Prior Art
A conventional color printer of a type prints out an image displayed on a color display unit. In this case, the printer converts an RGB (red, green and blue) signal for display supplied from an external apparatus such as a computer or the like into a YMC (yellow, magenta and cyan) signal for print and then records respective colors on the basis of the converted signal.
An example of the method of generating a YMC signal from an RGB signal as described above is disclosed in Japanese Patent Application Disclosure No. Hei 1-97652. A prior art method disclosed in the reference is described below with reference to FIG. 4.
FIG. 4A is a block diagram showing a main part of a printer implementing the above-mentioned method. When an RGB signal is inputted into an ink arranging section 401 shown in FIG. 4A, the ink arranging section 401 converts the RGB signal into a YMC signal and simultaneously applies a pseudo-toning process to the YMC signal with reference to a color conversion table 402 and then outputs it to a printing section 403. The printing section 403 performs printing according to the inputted YMC signal to perform color recording.
A simple example of the conversion process in the ink arranging section 401 is as follows: ##EQU1##
As an example of pseudo-toning processes, a case of performing a process using a threshold value matrix X of 4.times.4 (Bayer type) by means of a density pattern method is described with reference to FIGS. 4B to 4E.
When a original pixel data (any one color of Y, M and C) is "7" as shown in FIG. 4B, a sample value matrix where all values in a matrix of 4.times.4 are "7" is generated as shown in FIG. 4C. A matrix shown in FIG. 4E is obtained by comparing the generated sample value matrix with a threshold value matrix stored in advance in the color conversion table 402 shown in FIG. 4D. Hatched parts in the matrix shown in FIG. 4E are ones where the sample value matrix is greater than the threshold value matrix and YMC signals for printing are outputted. Namely, a signal of 16 dots (4.times.4) can be outputted for one original picture element, where the number of dots actually outputted out of the 16 dots corresponds to the tone of the original picture element.
The printing section 403 performs printing on the basis of YMC signals obtained as a result of the above-mentioned process. This printing is performed for each of the primary colors of Y, M and C to make a three-color superposed printing.
Since in the above-mentioned method the color mixture of the respective primary colors of Y, M and C is performed by parts where the colors are actually mixed and the other parts where the colors are placed side by side and as a result two methods being different in color mixture effect co-exist, its printing result can be different from the original image. In order to avoid such a problem, the above-mentioned prior art reference has disclosed a technique of finding the optimal areas of the mixed colors obtained by the primary ink colors and their superposition and of a paper color corresponding to tristimulus values of the given RGB signals and setting these areas as output areas of the respective colors of Y, M and C. Namely, this is a method of reproducing an image by individually determining area rates in one pixel dot of the Y, M, C, R, G, B and K (black) colors made by combination of the inks of Y, M and C and a paper color W (white), and this method obtains the area rates of the Y, M, C, R, G, B and K (black) colors by solving the following expression: ##EQU2## where y, m, c, r, g, b, k and w are respectively area rates of the Y, M, C, R, G, B, K and W colors.
Since the prior art method produces the YMC signals used in printing on the assumption that printing paper is solid and white, there are the following problems:
In the case that paper on which predetermined lines, patterns or the like are recorded in advance is used as recording paper, since the grounding color is seen through, the part where the patterns or the lines have been recorded results in being seen as differently colored from the other part.
The above-mentioned phenomenon happens naturally also in case of performing printing on recording paper of an other color than white, and a reproduced image comes to be different in color from an image printed on white recording paper and as a result the color of the printed image becomes different from that intended. Particularly, it can be said that printing on paper of a deep color is hardly possible.
An object of the present invention is to provide a color recording method and a color printer capable of removing the above-mentioned disadvantages and reproducing colors with fidelity regardless of the kind of recording paper and performing natural printing also on paper other than solid paper.